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| Homebrew 5 MHz https://hamradiodeals.co.uk/forums/viewtopic.php?f=59&t=38767 |
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| Author: | M0JSW [ Sun Jan 06, 2013 6:16 pm ] |
| Post subject: | Homebrew 5 MHz |
I have been interested in homebrewing a simple rx/tx for some of the 5MHz allocation,but have held off as i`m concerned about straying outside the allotted frequencies.Would I be able to use a DSB transmitter or would this take me "out of band" ,as it were,on the spot frequencies? I have a couple of crystals for 5 megs and am considering a simple single channel rx/tx for using digimodes mainly Any suggestions gratefully recieved...  Jes
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| Author: | G6CSL [ Sun Jan 06, 2013 6:20 pm ] |
| Post subject: | Re: Homebrew 5 MHz |
No, you are OK. DSB and even AM are OK, and with rocks you will be OK frequency-wise. Here's the unofficial allocations. The 'whiteboard' is what you want. http://homepage.ntlworld.com/wadei/UK_6 ... zation.htm Go Jes 
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| Author: | M0JSW [ Sun Jan 06, 2013 6:52 pm ] |
| Post subject: | Re: Homebrew 5 MHz |
Thanks for the link Chris.I hav`nt looked properly at the new allocations yet but at first glance it looks like one of my Xtals is smack bang in the middle of the suggested digimode section.....sweeeet! I have a kit that has been modded so much that I am now repairing,repaired tracks,so I was thinking of stripping all the parts off and rebuilding it ugly style.Just need to find info on rx/tx filtering for 5 megs. |
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| Author: | G6CSL [ Sun Jan 06, 2013 6:56 pm ] |
| Post subject: | Re: Homebrew 5 MHz |
1. Ugly is good. 2. 100 puff across 11uH is five megs. Ring Spectrum. |
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| Author: | M0JSW [ Sun Jan 06, 2013 7:09 pm ] |
| Post subject: | Re: Homebrew 5 MHz |
G6CSL wrote: 2. 100 puff across 11uH is five megs. Cheers Chris.I assume thats the LPF value?....I`ve done the easy bit now.....applied for/recieved the nov so no excuses
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| Author: | G6CSL [ Sun Jan 06, 2013 7:57 pm ] |
| Post subject: | Re: Homebrew 5 MHz |
No, it's the BPF/oscillator tank value, as in 100 puff across an 11uH Toko coil. It actually comes in slightly lower, but it's well within the 'twiddle' range of the coil. Remember? ''One over two pi times square root LC' The problem being that a one Farad capacitor is the size of a bucket, and a one Henry coil is the size of an articulated lorry, so I do it the kid's way and just 'bounce' the decimal point left and fill the gaps with zeros. Then I use the windows calculator set to 'scientific' and just punch in all the zeros - pathetic. When you ring spectrum, remember that the guy has literally scoured the earth for them, so they are now 'Spectrum Coils' He's a bloody nice bloke though. |
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| Author: | M0JSW [ Sun Jan 06, 2013 8:44 pm ] |
| Post subject: | Re: Homebrew 5 MHz |
Thanks for that.I`ll dig my advanced book out again and look at the sums,I remember there being a decent section in there with the relevant formula. |
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| Author: | G6CSL [ Sun Jan 06, 2013 9:00 pm ] |
| Post subject: | Re: Homebrew 5 MHz |
It's a doddle, just do it the kid's way like I do. A millisomething is a thousandth. A microsomething is a millionth. A nanosomething is a billionth. A picosomething is a trillionth. So lets say you have a 100 picoFarad capacitor. Just write down 100 and then put a decimal point after it. Now move the decimal point to the left like the 'bouncing ball' in singalong movies. 10, 100, 1000, 10,000, 100,000 etc until you reach a trillion, then put a big dot there and fill in the gaps with zeros. Now count how many zeros. Now open your computer's calculator and switch to 'scientific'. Just press 'point', then tap in the required number of zeros, then 100, then 'times' and do the same with the inductor. Then square root it, times it by 6.284 and press 1/x to get the answer in Hertz. You will start doing it just for fun after a while.
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| Author: | G0BHD [ Sun Jan 06, 2013 10:18 pm ] |
| Post subject: | Re: Homebrew 5 MHz |
Or use the scientific functions key to raise to a minus power of ten! IE 10 to the minus 12 (10 pico farrads) 10 to the minus 6 (10 micro farrads) etc. Lot less zeros on the screen!
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| Author: | G6CSL [ Sun Jan 06, 2013 10:35 pm ] |
| Post subject: | Re: Homebrew 5 MHz |
Thanks, but you are forgetting one thing. You have a brain
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| Author: | G1HBE [ Mon Jan 07, 2013 9:28 am ] |
| Post subject: | Re: Homebrew 5 MHz |
After years of using 'one over2pirootLC', I stumbled across the following method: 1. Convert your frequency to wavelength 2. Divide by 2 3 The result is L in uH and C in puffs. Example: Say you want the values of L and C to come up on 3.7 MHz. Convert to wavelength which is 80. Divide by 2 = 40. That's 40uH and 40pf. If you end up with a rather poor L/C ratio, just fiddle with the values until it looks more betterer. In the above example you might want 80pf so you'd reduce L to 20uH. It sure beats rsing around and getting all legged-up with those 10-6's! |
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| Author: | G6CSL [ Mon Jan 07, 2013 12:14 pm ] |
| Post subject: | Re: Homebrew 5 MHz |
Now that is downright sneaky. It works though
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| Author: | G1HBE [ Mon Jan 07, 2013 1:00 pm ] |
| Post subject: | Re: Homebrew 5 MHz |
 It sure does, and so does this: if you have two known values and you want to know where they resonate, do this:25330/(L*C), then take the square root of the answer. Final answer is in MHz. Note L must be in uH and C in pf. Both methods are good enough to get you within twizzing distance, which is what counts. |
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